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Trying to understand HDR advantages

bobthemagicmoose

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I am relatively proficient at photography and have been doing HDR pictures for about 10 years. Perhaps because of this, I'm not sure I understand the benefits of HDR TV's.

In short: Does HDR just mean smoother color gradients or does it also include a higher degree of total range (brighter whites, darker blacks).

Here's what I mean:

Let's pretend there's a real-world scene with a very bright sky and very dark shadow. Let's say the sky has a brightness of 1000 and the shadow has a brightness of 0. Now let's say our eyes can cover most of that - let's say 10-990. When a cinematographer takes a video of this scene and it get's projected to my TV, let's say the ultimate image has a range of brightness 100-500. This means that the original scene shadows below 100 get crushed and all a represented at 100 and the sky between 500-1000 are all washed out, getting a value of 500. Now let's say a standard dynamic range TV has 10 distinct values (100, 150, 200, ... , 500). If an HDR TV has 100 distinct values (100, 105, 110, ... 500) it still doesn't increase the total range of the TV, just makes it so there aren't 'jaggies' in a gradient. Do HDR TVs necessarily mean a higher total contrast range?

Since I have no capability to determining the difference between 256 values of gray, I don't see how upping that number to 1028 would be a benefit.
 

why_wolf

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From what I can tell HDR seems to mean in general that the screen just has better color reproduction (wider pallet) than previous models. Supposedly it should also mean better contrast as well (a different method of back lighting to reduce light bleeding), though contrast ratings on TVs are frankly garbage.
 

cryoburner

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You can certainly see more than 256 shades of gray. It's just that the level of contrast between the brightest white and the darkest black on most displays isn't enough to make that particularly noticeable in most scenarios. However, if you were to make the screen capable of displaying brighter and/or darker colors, you'll increase the range between those maximum and minimum values, and in turn increase the difference between one shade of gray and the next.

If you're converting an HDR image to be displayed on standard 8-bit per pixel screens, you have to make some compromises and compress parts of the color range down, but if the screen can display a wider color range, you don't need to throw away as much data. The bright parts of the image can be displayed brighter than on a typical screen, but without changing the brightness and contrast of the midtone values, for example, which could retain their full color range.

Now ideally, HDR displays should have brighter whites and/or darker blacks along with a wider color space to include additional, more vibrant colors than what can be found in SRGB. Currently, we are in the early days of HDR screens though, so there will tend to be a lot of variance among how well these things are implemented, so not all screens will do this particularly well.
 

bobthemagicmoose

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Good point about being able to discern more shades of gray - I meant on any TV I've seen. But maybe if they were just straight bands of gray I would see the lines.

So it seems like HDR by itself doesn't mean a wider range - but typically most displays have a wider range to make use of the extra 2 bits. I really wish there were better ways of standardizing a tv's range so that we get meaningful contrast values - especially for rather close pixels.

Thanks for the input folks!
 

bobthemagicmoose

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Thanks americanaudiophile, that answered my question perfectly. For others that might be interested, the key take away is:
"Since manufacturers aren't obliged to reveal the number of nits (brightness) their screens achieve or the contrast ratio it's up to them to decide for themselves if a non-Premium screen has enough brightness and contrast to deliver a meaningful HDR image."

And, a "key metric for a[n ultra HD] Premium-badged panel is a contrast ratio of at least 1,000 nits peak brightness and less than 0.05 nits black level." ... But other hdr types are up to the manufacturers discretion.
 
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